Data from: Various competitive interactions explain niche separation in crop-dwelling web spiders

Competition for resources is a major organizing principle in communities of organisms that share similar ecological niches. Niche separation by means of exploitation or interference competition was investigated in two taxa of crop-inhabiting spiders that overlap in microhabitat use and have similar web design. Competition for prey and web sites was tested in microcosm experiments with the most common species that build sheet-webs: Enoplognatha gemina (Theridiidae) and Alioranus pastoralis (Linyphiidae). A field survey over the crop season provided data on spatial and temporal dispersion of Enoplognatha spp. (Theridiidae) and linyphiid spiders (Linyphiidae) and on availability of prey over the season. In the microcosm experiments, both taxa took springtails as prey, but only Enoplognatha fed on aphids. Differences in diet, however, could not be attributed to either exploitative or interference competition. Spatial separation of websites was attained by vertical displacement of webs in the vegetation (Enoplognatha) and by avoidance of patches occupied by conspecific or heterospecific individuals (linyphiids). In the field, densities of linyphiids and Enoplognatha were correlated negatively and webs were over-dispersed relative to a random distribution. Both taxa colonized the field at the start of the season; linyphiids colonized as adults, quickly reproduced, and had a second adult peak; Enoplognatha matured in the middle of the season and their numbers remained fairly constant over the season. The combined experimental manipulations and field data suggest that niche separation occurs at different scales. The hypothesis of competition for websites was partially supported, while prey preference (or tolerance) and temporal differences in life history stages also may explain the negative correlations between densities of the two taxa.资源竞争是共享相似生态位（ecological niche）的生物群落的核心组织原则之一。本研究针对两种微生境利用重叠、结网模式相似的农田栖息蜘蛛类群，探讨了通过利用性竞争（exploitation competition）或干扰性竞争（interference competition）实现的生态位分化（niche separation）现象。针对猎物与结网位点的竞争，本研究通过微宇宙实验（microcosm experiments）对两种常见片网（sheet-webs）结网蜘蛛进行了测试：宝石壮蛛（Enoplognatha gemina，球蛛科Theridiidae）与牧场阿奥蛛（Alioranus pastoralis，皿蛛科Linyphiidae）。本研究在作物生长季开展了野外调查，获取了壮蛛属物种（Enoplognatha spp.，球蛛科Theridiidae）与皿蛛科（Linyphiidae）蜘蛛的时空分布格局数据，以及整个生长季的猎物可获得性数据。微宇宙实验结果显示，两类蜘蛛均以弹尾虫（springtails）为猎物，但仅壮蛛属物种取食蚜虫（aphids）。然而，二者的食性差异无法归因于利用性竞争或干扰性竞争。两类蜘蛛的结网位点空间分化通过两种方式实现：壮蛛属物种通过在植被中垂直移动结网位置，而皿蛛科蜘蛛则通过避开被同种（conspecific）个体或异种（heterospecific）个体占据的生境斑块（patches）。野外调查结果显示，皿蛛科蜘蛛与壮蛛属物种的种群密度呈显著负相关，且结网位点的分布相对于随机分布呈集群分布（over-dispersed）。两类蜘蛛均在作物生长季初期定植至农田：皿蛛科蜘蛛以成虫态定植，快速繁殖并出现第二个成虫高峰；壮蛛属物种则在生长季中期成熟，其种群数量在整个生长季内保持相对稳定。综合实验操控与野外调查数据可知，生态位分化在不同尺度上均有发生。结网位点竞争假说得到了部分支持，而食性偏好（或耐受性）以及生活史（life history）阶段的时序差异，同样可以解释两类蜘蛛种群密度间的负相关关系。